E3, forget it, Nintendo never anounces in first hand Pokemon games, at least the main series, it'll be anounced first on Japan. Now Looking at DS timeline wich is almost the same every generation only changes 3rd spin to remake sometimes, it's allaways the same timeline, in DS we got (Japan dates):
2006 - Diamond/Pearl
2008 - Platinum
2009 - Heart Gold/Soul Silver
2010 - Black/White (new gen)
Then we can assume that it's now 2 years later Black and White, it's time for third spin:
2012 - 3rd spin - Pokémon Grey?
2013 - RSE remake
2014 - 4 years later 6th gen ?!
Platinum has been anounced/revealed in May, Heart Gold Soul Silver has been anounced/revealed in May to, and Black and White to, so if i'm not mistake it will be revelaed in May.
Looking back again, to 2008, Giratina new form was revealed in begining of 2008 for it's upcoming movie that was released in July on Japan, than May they've anounced Platinum, in July Giratina movie came out, and in september Platinum was released.
This year the movie will feature Kyurem, a japanese magazine said that in february or March, i'm not sure now about wich month they're talking about, they will anounce a "new" Pokémon, i bet it is Kyurem new form, then in may they should anounce 3rd spin Pokémon Grey featuring Kyurem, July the Kyurem movie will came, and then September it came out in Japan.
It will be for sure for 3DS, because Game Freak has 3DS devkit since end of 2009 and in the beggining of 2010 they recruited 3D game designers. And Nintendo wants to push 3DS, so makes no sense release it for DS.
PS: Sorry for my bad english
